The general construction of a known copyable blackboard is illustrated in FIG. 7. A written member 101 comprises a sheet, and 102 and 103 are winding rollers for the written member 101. Furthermore, 104 is a light source, 104 is a light collecting and reflecting mirror, 105 an optical path, the 106 an optical lens, the 107 a CCD image sensor, the 108 a printer, the 109 a board, the 110 a data memory, and the 111 a signal processing circuit.
In this construction, light is irradiated from the light source 104 onto the wound written member 101, and the light reflected therefrom is transmitted onto the CCD image sensor 107 through the optical lens 106 to be focused thereon. In the CCD sensor 107, signal charges which correspond to the light signal converted electrically and stored at the photo diode array are transferred to the CCD analog register to be output as a digital signal successively. This signal is processed or written in into memories, and thereafter sent to the printer 108 as a digital signal. In this printer 108 the picture information such as characters or figures depicted on the written member 101 are output on selected recording paper for example by a heat-sensitive recording method or an electronic photo copying method.
Furthermore, in the exemplary construction illustrated in FIG. 8 a control circuit is provided in addition to the construction of FIG. 7. In FIG. 8, the same reference numerals are used to designate the same or corresponding portions as those shown in FIG. 7. 132 designates an image memory apparatus, 133 an element peripheral circuit, the reference numeral 134 a control circuit, 136 a printing head, the 137 a platen roller, and the 138 a recording paper.
The operation of this copyable blackboard will be described below.
At first, characters or figures are depicted by written members such as a felt pen on the written member 101 which is held in tension and thus provided as a screen. Thereafter, when a predetermined copy button is pushed in order to make a photo copy, the written member 101 is wound around the roller 102 by driving the motor 102', and the light source 104 is switched on so that the emitted light may be irradiated onto the written member 101. This irradiated light is received by a light/electricity conversion element 107 (generally a CCD image sensor is used therefor) through the optical path 105, and the picture information detected by this light/electricity conversion element 107 is stored in the image memory device 132 through the peripheral circuit 133 and the control circuit 134, while it is sent to the printing head 136 through the printing control circuit 135, and it is recorded on the recording member 138 on the platen roller 137 by the printing head 136. Furthermore, the same content can be copied a plurality of times by specifying the number of copies desired during the button switch operation at the start. Then, the picture information stored in the image memory device 132 is sent to the printing head 136 through the control circuit 134, and the printing is effected on the recording member 138 the instructed number of times.
In the prior art copyable blackboard with such a construction, however, a reading section such as the CCD image sensor 107 and an output apparatus such as the printer 108, comprising for example the printing head 136, and the platen roller 137 are required in order to obtain copies of picture information of the written member 101. This makes the structure a complicated one, which leads to an increase in the production cost. Furthermore, a complicated control mechanism such as one including the image memory apparatus 132 is required in order to obtain a plural number of copies, which leads to a further increase in the production cost.
Furthermore, in the prior art copyable blackboard, the picture information on the written member is read out by the reading element such as a CCD image sensor to be converted into a digital signal, and the picture takes in the form of a dot matrix. This results in difficulty in obtaining a clear copied image. That is, the picture information detected by this sensor is output simply as a two-value signal of white and black, and therefore there arises disadvantage that the quality of the copied picture is poor due to reading skip of the respective picture elements and the batter of the picture element.
On the other hand, in order to obtain a high quality clear picture with a simplified structure, it is believed to be preferable to adopt a method of directly copying the picture information from the written member onto the recording member without using elements such as CCD image sensors. However, in this direct copying method high sensitivity recording paper such as heat developing type silver salt photographic paper cannot be used because of the fear of unexpected light exposure, and conventionally only photosensitive carbonless paper or diazo-photosensitive paper was used which has only one several tenth to one several thousandth of the photosensitivity of the heat developing type silver salt photographic paper. Therefore, a long exposure time is required and the copying speed is quite low. In order to enhance this copy speed it is required to use a light source of quite a high illumination but this leads to an extraordinary power consumption.